The invention relates generally to optical modulator devices and, more particularly, to an apparatus and method of forming a high performance, integrated optical module.
An electro-optic modulator (EOM) is an optical device in which a signal-controlled element exhibiting an electro-optic effect is used to modulate a beam of light. The modulation may be imposed on the phase, frequency, amplitude, or direction of the modulated beam. Optical transmission systems operating on frequencies exceeding 10 gigabits per second (Gb/s) are possible with the use of EOMs. Electro-optic modulators have applications in many types of products including, for example, Magnetic Resonance Imaging (MRI) receive coil arrays, ultrasound probes, and radio frequency transmission systems, to name a few.
One specific type of EOM includes a crystal material, such as lithium niobate (LiNbO3), whose refractive index is a function of the strength of the local electric field. Accordingly, if lithium niobate is exposed to an electric field, light will travel more slowly through the material. Therefore, the phase of the light exiting an EOM may be controlled by changing the electric field in the crystal. An electric field may be generated placing a parallel plate capacitor across the crystal. Since the field inside a parallel plate capacitor depends linearly on the potential, the index of refraction of the crystal generally depends linearly on the field. In turn, since the phase depends linearly on the index of refraction of the crystal, the phase modulation of the light passing through the crystal is controllled by the potential applied to the EOM.
In practical EOM devices, amplitude modulation is more commonly implemented through the use of a Mach-Zehnder (MZ) interferometer, in which a beam splitter divides an input optical signal into two paths (one of which includes a phase modulator as described above), and then recombines the two beams. By changing the electric field on the phase modulating path, it is possible to control whether the two beams constructively or destructively interfere, and thereby to control the amplitude or intensity of the exiting or output light.
LiNbO3 modulators are typically connected to radio frequency (RF) or microwave circuits via external electrical connections (e.g., discrete cable assemblies) between separately packaged lithium niobate and RF circuits. In some cases, RF circuits have been co-packaged with modulators with the various interconnections between parts made using wire bonds. However, RF performance degradations such as loss, reflections, and high frequency amplitude roll off occur most frequently at electrical interfaces between such packaged parts. Accordingly, it would be desirable to be able to implement an improved interface solution between EOMs and RF control circuitry.